This invention relates generally to a liquid level sensor and, in particular, to an engine oil level sensor which is automatically aligned in proper operating position by the force of gravity.
Over the past decade, there has been an ongoing endeavor by the industry to reduce the maintenance associated with automobiles. For example, some engines now include electronic ignition systems and computer controlled fuel injection systems which do not require any regular 15 maintenance or adjustments. Due to these recent improvements, there has been a tendency for vehicle owners to forget about certain critical engine maintenance functions which still must be performed, such as changing of the engine oil and engine coolant, and maintaining the engine oil and coolant at the proper levels between fluid changes. Moreover, due to the recent increase in number of self service gas stations and the reduced number of full service gas stations, engine oil and coolant levels are not checked by the vehicle operators on a regular basis. Accordingly, automotive manufacturers have found it desirable to incorporate fluid level sensors in order to provide an indication to the vehicle operator when the level of a particular fluid is low.
The prior art has proposed numerous types of liquid level sensors for sensing levels of various types of liquids For instance, U.S. Pat. No. 2,116,425 discloses a float switch for a refrigerant casing. The switch carries a horseshoe magnet on a pivotally mounted float to contact a pair of low-reluctance plugs at extremes of its motion. The plugs in turn attract one end or the other of a pendulum-shaped switch element, causing operation of electrical contacts.
U.S. Pat. No. 2,577,165 discloses a float switch for a pressure chamber such as a boiler. The switch uses a pair of permanent magnets to transmit the mechanical movement of a pivotally mounted float through a non-magnetic wall of a pressure chamber to operate a mercury switch.
U.S. Pat. No. 2,885,507 discloses a level indicating switch in which a conventional mechanically actuated switch is disposed in a flexible bag. The switch is operated by pressure applied against the bag by linkage connected to a pivotally mounted float which is responsive to the level of oil in an automobile automatic transmission.
More recently, liquid level sensors have incorporated magnetically-actuated reed switches. For example, U.S. Pat. No. 4,441,860 discloses a fluid level sensor using a reed switch and a two-part lost motion float, one part of the float either carrying a magnet to actuate the reed switch or carrying a soft iron member to complete a magnetic circuit to actuate the reed switch. The float is maintained in either of two vertical positions by the cooperation of magnets and soft iron to provide hysteresis in its operation.
However, the prior art devices typically require some form of careful alignment, so that the forces of buoyancy and gravity act in colinear opposition. The present invention overcomes this and other disadvantages of the prior art, as will be apparent from the description which follows.